A mana cost of means that you pay twice X. If you want X to be 3, you pay to cast Entreat the Angels.

3/14/2017

Entreat the Angels’s converted mana cost is based on its mana cost of , even if you’re casting it for its miracle cost. For example, if you cast Entreat the Angels for its miracle cost and choose 4 for X, its converted mana cost is 11.